Solid state power supply activated by a pyrotechnic chain

ABSTRACT

A two stage solid state power supply for apparatus such as a projectile fuze wherein a first piezoelectric device receives an initiating stress or shock wave upon firing the projectile. The first piezoelectric device then generates an electrical signal of a predetermined characteristic which is adapted to trigger a sequentially fired pyrotechnic chain of devices each having a predetermined time delay and which respectively generate second stress or shock waves which are directed to a second piezoelectric device. The second piezoelectric device will continuously generate electrical power for other fuze circuitry associated therewith until the last pyrotechnic device has ceased to generate its respective stress wave.

Sept. 4, 1973 1 SOLID STATE POWER SUPPLY ACTIVATED BY A PYROTECIINIC CHAIN Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thomas H. Webb [75] Inventors: Forrest E. England, Severna Park,

Md; Joseph IL Gifford Coral Attorney-F. H. Henson et a1.

F1 Sprmgs a 57 ABSTRACT [73] Asslgnee: Westmghouse Electnc Corpomuon, A two stage solid state power supply for apparatus such Pittsburgh as a projectile fuze wherein a first piezoelectric device 22 il July 30 1971 receives an initiating stress or shock wave upon firing the projectile. The first piezoelectric device then gener- [211 App! 167,576 ates an electrical signal of a predetermined characteristic which is adapted to trigger a sequentially fired pyro- 52 us. c1. 102/70.2 R, 102/702 GA teehhie ehaih of deviees eeeh having a predetermined 51 1m. 01. F42c 11/02, F42c 15/40, F421: 19/12 time delay and whieh respectively generate second 158] Field 01' Search 102/702, 28 stress of Shock Waves which are directed to a Second piezoelectric device. The second piezoelectric device 5 References Cited will continuously generate electrical power for other UNITED STATES PATENTS fuze circuitry associated therewith until the last pyrotechnic device has ceased to generate its respective 3,351,016 11/1967 Simpson .1 102/702 Stress wav 3,589,294 6/1971 Stresau 102/702 A 3,653,324 4/1972 Furlani et a] l02/70.2 R 10 Claims, 3 Drawing Figures LOGIC 301 B 30 INITIATING STRESS WAVE PYROTECHN IC STRESS WAVE 2 FUZE ELECTRONICS Cl RCUITRY PATENTED SE? 4 I975 PR TECHNIC RGES Q LOGI INIT T STRESS WAVE SOLID STATE POWER SUPPLY ACTIVATED BY A PYROTECIINIC CHAIN The inventi herein described was made in the course of or under a contract or subcontract thereunder, or grant with the US Army Material Command under Contract DAAG39-70-C-00l 3.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to electrical power supply apparatus and more particularly to a power supply utilized for powering a one-shot device having a relatively short useful life such as for example a projectile fuze.

2. Description of the Prior Art Fuzes on modern weapons tend toward use of sophisticated electronics for detonating the weapon under predetermined conditions after firing. While the electronics portion of the fuze can be packaged in a very small space, the power sources usually require the bulk of the space available. As the state of the art in packaging advances, the power source nevertheless remains the greatest space user.

Some thought has been given to utilizing the strain energy stored in the projectile from the base pressure which propels it from a gun barrel. The method of extracting this energy in useful form is to insert a piezoelectric wafer between the shell and nose piece to introduce the energy output to a power conversion system. A problem which becomes evident, however, is that the dynamic range required of the device is too large for its capability. For instance, in order to obtain a sufficient output at low base pressure, the design parameters would cause the wafer stress to be excessively high when the base pressure on the projectile is near its highest possible value. Additionally, the base pressure variations can occur as a result of standard operation. That is, range requirements can change from round to round or from weapon to weapon whereas the same fuze must operate on all such rounds.

SUMMARY The present invention comprises a power supply pyrotechnically energized for powering electronics circuitry and comprises two stages. The first stage contains a first piezoelectric wafer coupled to a logic circuit and an ignition squib. The second stage contains a second piezoelectric wafer and a plurality of small pyrotechnic charges interconnected so as to provide a series circuit of sequentially fired charges having a fixed time delay between each charge. An initiating stress or shock wave is applied to the first piezoelectric wafer which provides an electrical signal output which is coupled to the logic circuit where the waveform is measured for preselective characteristics. In the event that such characteristics exist, the logic circuit provides an output which fires the ignition squib. The squib in turn sets off the first pyrotechnic charge which develops a stress wave which is directed to the second piezoelectric wafer whereupon the second piezoelectric wafer develops an electrical voltage which is coupled to the electronics circuitry which includes power conversion components or elements. The second stage, moreover, is shock isolated from the surrounding environment so that the second piezoelectric wafer cannot be affected by the initiating stress wave.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partially in section of an ammunition round including a fuze powered by a piezoelectric wafer;

FIG. 2 is a view partially in section of an ammunition round including a fuze powered by the preferred embodiment of the subject invention; and

FIG. 3 is a schematic diagram of the preferred embodiment of the subject invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and more particularly to FIG. 1, there is shown the basic concept of a means for powering a projectile fuze which includes an electronics package for detonating an ammunition round. Accordingly, a reference numeral 10 designates the base of an ammunition round which includes the explosive not shown and reference numeral 12 designates a detonating fuze mounted on the forward portion of the base 10 in a manner well known to those skilled in the art. The fuze 10 includes electronics circuitry 14 which operates to detonate the ammunition round once it has been fired and thereafter comes into proximity of a target. As noted above, the majority of the space in the relatively small enclosure of the fuze is taken up by the power source. The present invention has for its object the use of a piezoelectric device such as a wafer 16 to power the electronics circuitry 14. It is well known that piezoelectric crystals such as quartz, tourmaline and Rochelle salt exhibit a characteristic known as the piezoelectric effect which is the property of the crystal by which mechanical stresses produce electric charges and conversely electric charges produce mechanical stresses. Accordingly, it is theoretically possible that the strain energy stored in the projectile from the base pressure occurring as a result of the ammunition round being fired from a gun barrel can be directed to the piezoelectric wafer 16 whereupon the electrical energy produced as a result of the vibration set up therein is applied to the electronics circuitry 14 as a supply voltage or one which can be converted to a useful supply voltage. Although such an embodiment as shown in FIG. 1 appears to be feasible, certain limitations pointed out earlier appear to render such a simple embodiment an impracticality.

The subject invention provides a means whereby the general concept of utilizing a piezoelectric device to power an electronics package is incorporated in a proximity fuze for projectiles wherein a single relatively short useful life is encountered. The preferred embodiment of the subject invention is shown in FIGS. 2 and 3 wherein FIG. 2 generally discloses the relative physical location of elements while FIG. 3 discloses a schematic of the present invention. Two stages, each of which contain a piezoelectric device act in combination to provide electric power to the fuze electronics circuitry generally designated by reference numeral 14. The first stage is comprised of a first piezoelectric wafer 20 coupled by means of logic apparatus 22 to an ignition squib 24. The first piezoelectric wafer 20 is adapted to receive an initiating stress or shock wave which would be coupled thereto, for example, upon the firing of the projectile. This piezoelectric wafer may be located, for example, between the shell base 10 and the proximity fuze body 18 or at the rear of the fuze body as shown in FIG. 2. Due to the fact that the base pressure on the projectile is of a very relatively high value and may vary depending upon the desired operation and/or mission capability, it is possible that the first piezoelectric wafer 20 may be rendered inoperative or destroyed after the initial stress wave is received. However, an electrical signal output will be provided initially by the wafer 20 which is first coupled to the logic apparatus 22. The purpose of the logic device is to distinguish between a piezoelectric output due to an actual firing and various' other shock inputs which would be encountered for example during handling as well as dropping. The logic device 22 is adapted to discriminate between amplitude variations as well as the wave shape of the electrical output of the wafer 20, thus providing a needed safety feature. Assuming that a firing has occurred and the logic device 22 senses a firing type of signal coupled thereto, it only then couples a signal to the ignition squib 24 which is a small triggering type pyrotechnic device. The function of the first piezoelectric wafer 20, therefore, is to provide sufficient energy from a first predetermined type stress impulse that reaches it to power the logic circuitry and fire the squib 24 if the logic permits.

The second stage includes a housing 26 which is shock isolated from the remainder of the fuze body 18 by suitable means 27 and includes therein a second piezoelectric wafer 28 and a plurality of small pyrotechnic charges 30,, 30 30 30,, and 30, contained in a package 31, which are coupled together in series so that they fire sequentially with a fixed time delay between each charge. The squib 24 when it is ignited is coupled to the first charge 30 which generates a stress wave directed to the second piezoelectric wafer 28. The wafer 28, in turn, produces an electrical output due to the effect of the stress wave which is coupled by circuit means 29 back to the fuze electronics circuitry 18 which includes conversion circuitry, not shown, for energizing the remainder of the fuze circuitry for accomplishing the desired mission, that is, selectively detonating the round when predetermined conditions exist after a predetermined time delay. A short time after the firing of the first charge 30 the second charge 30, is fired which again applies a stress wave to the wafer 28 and so on. It can be seen, therefore, that the function of the second stage is to provide continuous power from the second piezoelectric wafer 28 as it responds to a series of periodic impacts introduced by the time series delay pyrotechnic charges 30 30,

The advantage of the preferred embodiment of the subject invention shown in FIG. 3 is that a uniform maximum stress level can be obtained for the second stage piezoelectric wafer 28 from round to round irrespective of the variation in the maximum base pressure encountered from round to round or from one weapon to another. This is accomplished through the design of the delay train of the pyrotechnic charges by a manner well known to those skilled in the art. This assures a maximum output without the possibility of depolarizing or structurally damaging the wafer 28. A damaging stress level within the first stage piezoelectric wafer 20 is of no consequence because it merely acts as a triggering mechanism. If the round encountered a severe accidental drop, the damage would be extensive enough to be recognized and the projectile discarded. Secondly,

the projectile and fuze could survive routine accidental drops without firing because the stress levels would not be high enough to damage the first stage piezoelectric wafer and outputs from the first stage would be blocked from igniting a second stage by means of the logic circuitry 22. Thirdly, the power can be generated over an extended period of time with the preprogrammed pyrotechnic chain 30 30,. The stress oscillations resulting from the intial firing would die out too quickly to provide sufficient energy for a long period of time whereas the clean up function after a long duration could be accommodated with the pyrotechnic chain and the second stage peizoelectric wafer acting as an energy source.

What is shown and described, therefore, is apparatus which achieves a uniform peak level of stress on a piezoelectric device contained therein for the purpose of generating electrical power where the input stress levels have a relatively wide dynamic range such as in an artillery fuze employing solid stage devices.

Having disclosed what is at present considered to be the preferred embodiment of the subject invention, we claim as our invention:

1. A source of electrical energy adapted to power electronic circuitry comprising in combination:

first peizoelectric means responsive to stress impulse waves to produce electrical output signals and producing a predetermined output signal in the event that a first type stress impulse wave impinges thereon;

logic means coupled to said first piezoelectric means and being responsive to said electrical output signals to provide a trigger signal when said predetermined output signal is coupled thereto;

means coupled to said logic means being energized by said trigger signal to provide a firing output signal therefrom which is adapted to fire a pyrotechnic device;

a plurality of pyrotechnic means coupled together in series to said means coupled to said logic means, being ignited after said firing output signal is applied to the first of said plurality of said pyrotechnic means wherein each of said means then sequentially fires after a predetermined time delay to pro duce a series of tiem delayed stress impulse waves; and

second piezoelectric means selectively located relative to said plurality of pyrotechnic means so as to receive the series of time delayed stress impulse waves produced thereby to generate an electrical signal during the time period during which said plurality of pyrotechnic means sequentially ignite.

2. The apparatus as defined by claim 1 and additionally including shock isolation means surrounding said plurality of pyrotechnic means and said second piezoelectric means for insulating said pyrotechnic means and said second piezoelectric means from said first type stress impulse wave.

first and second piezoelectric means comprises piezoelectric wafers.

9. The apparatus as defined by claim 8 wherein said means coupled to said logic means comprises a firing squib.

10. The apparatus as defined by claim 9 wherein said first piezoelectric means is located in the rearward portion of said body portion. 

1. A source of electrical energy adapted to power electronic circuitry comprising in combination: first peizoelectric means responsive to stress impulse waves to produce electrical output signals and producing a predetermined output signal in the event that a first type stress impulse wave impinges thereon; logic means coupled to said first piezoelectric means and being responsive to said electrical output signals to provide a trigger signal when said predetermined output signal is coupled thereto; means coupled to said logic means being energized by said trigger signal to provide a firing output signal therefrom which is adapted to fire a pyrotechnic device; a plurality of pyrotechnic means coupled together in series to said means coupled to said logic means, being ignited after said firing output signal is applied to the first of said plurality of said pyrotechnic means wherein each of said means then sequentially fires after a predetermined time delay to produce a series of tiem delayed stress impulse waves; and second piezoelectric means selectively located relative to said plurality of pyrotechnic means so as to receive the series of time delayed stress impulse waves produced thereby to generate an electrical signal during the time period during which said plurality of pyrotechnic means sequentially ignite.
 2. The apparatus as defined by claim 1 and additionally including shock isolation means surrounding said plurality of pyrotechnic means and said second piezoelectric means for insulating said pyrotechnic means and said second piezoelectric means from said first type stress impulse wave.
 3. The apparatus as defined by claim 1 wherein said means coupled to said logic means comprises an ignition squib.
 4. The apparatus as defined by claim 1 wherein said first and second piezoelectric means comprises a wafer of piezoelectric material.
 5. The apparatus as defined by claim 1 and additionally including artillery projectile fuze means coupled to and powered by said second piezoelectric means.
 6. The apparatus as defined by claim 5 wherein said fuze means additionally includes a body portion for attachment to a projectile base and wherein a firing of said projectile base with said body portion attached thereto causes said first type stress input wave to be directed to said first piezoelectric means.
 7. The apparatus as defined by claim 6 and additionally including means for shock isolating said plurality of pyrotechnic devices and said second piezoelectric means from said body portion.
 8. The apparatus as defined by claim 7 wherein said first and second piezoelectric means comprises piezoelectric wafers.
 9. The apparatus as defined by claim 8 wherein said means coupled to said logic means comprises a firing squib.
 10. The apparatus as defined by claim 9 wherein said first piezoelectric means is located in the rearward portion of said body portion. 